Support body for semiconductor element, method for manufacturing the same and semiconductor device

ABSTRACT

A semiconductor device comprising the semiconductor element and the support body made of a stack of ceramics layers having a recess in which a electrical conductors are electrically connected with the semiconductor element, wherein at least a part of the top face of the recess side wall is covered by a resin, thereby providing a light emitting device of high reliability.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing a support body made of ceramics whereon a semiconductor element, particularly a semiconductor light emitting element can be mounted, and to a semiconductor device that employs the support body made of ceramics.

2. Description of the Related Art

A support body made of ceramics for mounting a semiconductor element has been manufactured by stacking ceramics layers that have not yet been fired, called the ceramics green sheets, forming through holes in the stack, making electrical wiring to connect the semiconductor element and firing the stack. At the time when the ceramics green sheets have been stacked, cleaving lines are drawn so the stack of ceramic green sheets that has been fired can be cleaved by applying a force in a particular direction and separated into individual ceramics packages (refer, for example, to Patent Document 1).

The support body made of ceramics is superior in heat dissipation and heat resistance than packages made of plastics, and enables it to make a light emitting device capable of emitting light of high luminance over a long period of time when a semiconductor light emitting element is mounted thereon. This makes it possible to use the light emitting device as the light source of backlight for a liquid crystal display, and demands are increasing for thinner and smaller light emitting devices. One of such light emitting devices that satisfy the demand is sideways emission type light emitting device (refer, for example, to Patent Document 2). The sideways emission type light emitting device is mounted and connected to a substrate having electrically conductive wiring pattern by soldering, after undergoing a process called reflow, so that light is emitted along an optical axis substantially parallel to the mounting surface thereof.

[Patent Document 1]

Japanese Unexamined Patent Publication (Kokai) No. 52-58468

[Patent Document 2]

Japanese Unexamined Patent Publication (Kokai) No. 2003-168824

However, since the support body made of ceramics used in the sideways emission type light emitting device described above is made by firing a stack of ceramic green sheets in mass production, cleavage surface of the ceramics stack formed when separating it into individual support bodies made of ceramics must be used as the mounting surface for the light emitting device. This results in problems including the following major ones: (1) burrs and/or chippings are caused when cleaving the stack into individual support bodies; (2) cleavage surfaces cannot be made invariably smooth because burrs and chippings generated in the cleavage surface differ from chip to chip; and (3) the angle between the cleavage surface and the light emitting surface differ from chip to chip. The cleavage surface having such problems as described above causes variability in the optical characteristics of the device when the light emitting device is mounted on a circuit board to make an optical device.

The support body made of ceramics used to make the sideways emission type light emitting device as described above has electrical wiring formed on the mounting surface thereof adjacent to the light emitting surface. Moreover, the electrical wiring is connected to the electrical circuit formed on an external circuit board by soldering, so as to provide mechanical and electrical connection between the light emitting device and the external circuit board. However, there occur such problems as a part of the light emitting surface is covered by solder during the reflow process and/or short-circuiting occurs as solder lines which should be separated as positive and negative polarities in the circuit are brought into contact with each other, thus making it impossible to make light emitting devices of high reliability. When the quantity of solder used is decreased, sufficient electrical and mechanical connection may not be achieved between the light emitting device and the external circuit board. Possibility that the problems described above occur becomes higher when the support body is made of ceramics than when it is made of plastics, and higher when the support body is smaller.

SUMMARY OF THE INVENTION

Thus an object of the present invention is to provide a method of manufacturing a support body made of ceramics, particularly a support body made of ceramics used in a sideways emission type light emitting device, especially a manufacturing method that does not generate burr or chipping in the cleavage surface. Another object is to provide a light emitting device of high reliability by using the support body made of ceramics.

The present invention provides a support body on which a semiconductor element can be mounted, that is made by separating a ceramics substrate whereon electrical conductors are disposed, wherein a side face of the support body has a incised portion located on the side where the semiconductor element is to be mounted, and a portion cleaved substantially at right angles to the incised portion by applying a bending moment and a tensile force substantially simultaneously to the ceramics substrate, while the polished portion is in a range from ¼ to ¾ thickness of the ceramics substrate. The incised portion is more preferably in a range from approximately {fraction (1/20)} to {fraction (3/20)} of the thickness of the ceramics substrate. A bending moment and a tensile force that are applied substantially simultaneously mean a sequence of actions for separating the substrate and does not mean exactly simultaneous actions.

In the portion cleaved at right angles, it is preferable that a protruded portion protruding out from a vertical face extending vertically from the incised portion toward the opposite side to the side to be mounted with the semiconductor element are half of the thickness of the ceramics substrate or smaller in the portion cleaved at right angles.

The support body preferably has a recess in which a semiconductor element is placed, and the electrical conductor is disposed either in a part of or the entire recess.

The side face of the support body preferably has a metal disposed at least on one of the corners so as to extend from the surface where the semiconductor element is mounted to the back surface.

The present invention relates to a semiconductor device comprising a semiconductor element and the support body whereon the semiconductor element is mounted.

It is preferable that the support body has a recess in which a semiconductor element is placed, and the electrical conductor is disposed in a part of the recess, while the side face of the support body has a metal disposed at least on one of the corners so as to extend from the surface where the semiconductor element is mounted to the back surface, and the recess and top face of the recess side wall are covered with a resin.

The top face of the recess side wall is preferably covered with a resin in a portion of the ceramics base.

Inside of the recess and the top face of the recess side wall are preferably impregnated with a resin in a portion where the ceramics base is exposed.

The present invention relates to a method of manufacturing the support body whereon a semiconductor element can be mounted, comprising processes of making a ceramics substrate by stacking ceramics sheets with electrical conductors disposed thereon, incising the ceramics substrate thereby forming a groove, and cleaving the ceramics substrate along the grooves, wherein the ceramics substrate is cleaved by applying a bending moment and a tensile force to the ceramics substrate.

The bending moment is preferably applied by bringing a cleaving tool into contact with the surface opposite to the surface having the grooves of the ceramics substrate at a position corresponding to the groove.

The ceramics substrate may also be preferably cleaved by applying a bending moment in such a manner as the substrate becomes concave on the side thereof where the groove is formed so that the opposing top edges of the recess side walls make contact with each other.

The grooves of the ceramics substrate may also be formed in the longitudinal and lateral directions on the front surface, while through holes may be made at the intersects of the longitudinal and lateral grooves with the through holes filled with a metallic material to make electrical conductors.

The ceramics substrate may also be provided with a plurality of through holes along which the grooves are drawn on the surface of the ceramics substrate.

The ceramics substrate is fired to form a groove after incising the ceramics substrate to a depth in a range from ¼ to ¾ thickness of the ceramics substrate.

Such a process may also be employed as ceramics sheets having electrical conductors disposed thereon are stacked one on another to form a ceramics substrate having a recess formed therein, which is cleaved along grooves drawn along the side walls of the recess, thereby making the support body that have the electrical conductors exposed on the cleavage surface and in the recess.

In the semiconductor device comprising the semiconductor element and the support body made of a stack of ceramics layers having the recess wherein the electrical conductors are electrically connected with the semiconductor element, at least a part of the top face of the recess side wall is preferably covered by a resin.

The resin may also caused to further impregnate the ceramics base portion of the side wall of the recess.

It is preferable that the semiconductor element is coated with the resin and a part of the resin is disposed to extend over the top face of the recess side wall.

The resin preferably contains at least one kind of fluorescent material selected from among a fluorescent material that contains Al and at least one element selected from among Y, Lu, Sc, La, Gd, Tb, Eu, Ga, In and Sm, and is activated with at least one element selected from among rare earth elements, and a fluorescent material that contains N, at least one element selected from among Be, Mg, Ca, Sr, Ba and Zn and at least one element selected from among C, Si, Ge, Sn, Ti, Zr and Hf, and is activated with at least one element selected from among rare earth elements.

[Effect of the Invention]

The present invention provides a support body on which a semiconductor element can be mounted, that is made by separating a ceramics substrate whereon conductors are disposed, wherein a side face of the support body has a incised portion located on the side where the semiconductor element is to be mounted, and a portion cleaved substantially at right angles to the incised portion by applying a bending moment and a tensile force substantially simultaneously to the ceramics substrate, while the incised portion is in a range from ¼ to ¾ thickness of the ceramics substrate. With this constitution, the surface whereon the semiconductor element is to be mounted has uniform size because it is separated by the grooves. Also because the bending moment and the tensile force are applied substantially simultaneously, the support body can be made relatively easily without causing burrs or chippings in the cleavage surface. Keeping the incised portion small enables it to hold while the support body is allowed to have a large surface area on the side where the semiconductor element is mounted. In case a light emitting element is used for the semiconductor element, the light emitting device constituted by using the support body made of ceramics enables it to make an optical apparatus by mounting the semiconductor device on a circuit board without causing variability in the optical characteristics.

In the portion cleaved at right angles, it is preferable that a protruded portion protruding out from a vertical face extending vertically from the incised portion toward the opposite side to the side to be mounted with the semiconductor element are half of the thickness of the ceramics substrate or smaller in the portion cleaved at right angles. In a sideways emission type light emitting device in which the support body is used, if the protruded portion are half of the thickness of the ceramics substrate or smaller, a tilt on mounting is 30 degree or less. It is preferable that the protruded portion protruding out side are quarter of the thickness of the ceramics substrate or smaller. With this, the tilt on mounting is 15 degree or less. It is more preferable that the protruded portion protruding out side are {fraction (1/10)} of the thickness of the ceramics substrate or smaller. With this, a constant emitting angle is kept without notice of the tilt on mounting. Dent portion denting inside within about half of the thickness of the ceramics substrate or smaller may be allowed since the dent portion do not affect the tilt on mounting. However, from the viewpoint of productivity, the depth of the dent portion is preferably quarter of the thickness of the ceramics substrate or less, more preferably {fraction (1/10)} of the thickness of the ceramics substrate or less.

The support body has the recess for placing the semiconductor element therein, and the electrical conductor is preferably disposed on a part of or on the entire recess. This enables it to electrically connect with the semiconductor element. It is also made possible to electrically connect outside electrodes and the support body.

The side face of the support body preferably has a metal disposed at least on one of the corners so as to extend from the surface where the semiconductor element is mounted to the back surface. This enables it to secure a wide area of electrically conductive portion when mounting the support body by soldering.

The present invention relates to a semiconductor device comprising the semiconductor element and the support body whereon the semiconductor element is mounted. Thus such a semiconductor can be made having the support body with less burrs and chippings. The semiconductor device of the present invention can be mounted on a circuit board having electric wiring pattern formed thereon with high reliability.

It is preferable that the support body has the recess for mounting the semiconductor element therein, the electrical conductor is preferably disposed on a part of the recess, the metal is disposed at least on one of the corners so as to extend from the surface where the semiconductor element is mounted to the back surface, and the inside of the recess and the top face of the recess side wall are covered with a resin. Since the ceramics substrate is permeable to moisture and air, resin coating is provided so as to prevent permeation of such materials.

The top face of the recess side wall is preferably covered with a resin on a portion where the ceramics base is exposed, since it prevents solder from creeping up when the semiconductor element is mounted.

The portions of the inside of the recess and the top face of the recess side wall where the ceramics base is exposed is preferably impregnated with a resin, so as to prevent permeation of moisture and air, and prevent the solder from creeping up when mounting.

The present invention relates a method of manufacturing the support body whereon a semiconductor element can be mounted, comprising processes of making a ceramics substrate by stacking ceramics sheets with electrical conductors disposed thereon, forming grooves by incising the ceramics substrate, and cleaving the ceramics substrate along the grooves, wherein the ceramics substrate is cleaved by applying a bending moment and a tensile force to the ceramics substrate. With this method, the support body made of ceramics can be formed easily without causing burrs or chippings in the cleavage surface.

The bending moment is preferably applied by bringing a cleaving tool into contact with the surface opposite to the surface having the grooves of the ceramics substrate at a position corresponding to the groove. Since this enables it to separate the chips without causing the cleavage surfaces to rub against each other, quantity of ceramics powder generated when cleaving can be reduced. The cleavage surface of the separated ceramics substrate can also be formed substantially at right angles to the groove. Thus a number of support bodies can be made from a single ceramics substrate.

The ceramics substrate may also be preferably cleaved by applying a bending moment in such a manner as the substrate becomes concave on the side thereof where the groove is formed so that the opposing top edges of the recess side walls make contact with each other. With this method, the support body made of ceramics can be formed easily without causing burrs or chippings in the cleavage surface.

The grooves of the ceramics substrate may also be formed in the longitudinal and lateral directions on the front surface, while through holes may be made at the intersects of the grooves in the longitudinal and lateral directions with the through holes filled with a metallic material to make electrical conductors. The metallic material provided in the through hole is preferably connected with the electrode provided on the back surface. Thus the electrical conductor can be easily provided on the side face of the ceramics substrate. It is also made easy to locate the position where the though hole is to be formed.

The ceramics substrate may also be provided with a plurality of through holes along which the grooves are drawn on the surface of the ceramics substrate. While the through hole provided with the electrical conductor is formed on the ceramics substrate, forming the groove along the through hole makes it easier to cleave the ceramics substrate into individual ceramics packages.

The ceramics substrate is fired to form a groove after incising the ceramics substrate to a depth in a range from ¼ to ¾ of the thickness of the ceramics substrate. When the depth of the groove is shallow, burrs are generated. On the other hand, when the depth of the groove is deep, burrs tend to be easily generated on the cleavage surface because the ceramics substrate splits off easily by only applying a slight shock. It is hard to produce because of a risk of splitting off when removing from the die.

Such a process may also be employed as ceramics sheets having electrical conductors disposed thereon are stacked one on another to form a ceramics substrate having a recess formed therein, which is cleaved along grooves drawn along the side walls of the recess, thereby making the support body that have the electrical conductors exposed on the cleavage surface and in the recess. This method makes it possible to stably mount the support body on an external circuit board when the cleavage surface of the ceramics substrate is used as the mounting surface onto the circuit board.

In the semiconductor device comprising the semiconductor element and the support body made of a stack of ceramics layers having the recess wherein the electrical conductors are electrically connected with the semiconductor element, at least a part of the top face of the recess side wall is preferably covered by a resin, in order to prevent moisture from infiltrating.

The resin may also be caused to impregnate the top face of the recess side wall where the ceramics base is exposed. This makes it possible to prevent the solder from creeping up and make a semiconductor device of high reliability when mounting the semiconductor device on an external circuit board.

It is preferable that the semiconductor element is covered by the resin and part of the resin is disposed to extend over the top face of the recess side wall. This makes it possible to prevent permeation of moisture.

The resin preferably contains at least one kinds of fluorescent material selected from among a fluorescent material that contains Al and at least one element selected from among Y, Lu, Sc, La, Gd, Tb, Eu, Ga, In and Sm, and is activated with at last one element selected from among rare earth elements, and a fluorescent material that contains N, at least one element selected from among Be, Mg, Ca, Sr, Ba and Zn and at least one element selected from among C, Si, Ge, Sn, Ti, Zr and Hf, and is activated with at last one element selected from among rare earth elements. This constitution makes it possible to make a light emitting device that emits light by blending the light from the semiconductor light emitting element and the light emitted by a fluorescent material that is excited by the former.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic top view of one example of the semiconductor device of the present invention.

FIG. 1B is a schematic perspective view of one example of the semiconductor device of the present invention.

FIG. 2 is a schematic sectional view of one example of the semiconductor device of the present invention.

FIGS. 3A is a side view schematically showing the manufacturing process step 1 of the present invention.

FIGS. 3B is a side view schematically showing the manufacturing process step 2 of the present invention.

FIGS. 3C is a side view schematically showing the manufacturing process step 3 of the present invention.

FIG. 4A is a side view schematically showing the manufacturing process step 1 of the present invention.

FIG. 4B is a side view schematically showing the manufacturing process step 2 of the present invention.

FIG. 4C is a side view schematically showing the manufacturing process step 3 of the present invention.

FIG. 4D is a side view schematically showing the manufacturing process step 4 of the present invention.

FIG. 4E is a side view schematically showing the manufacturing process step 5 of the present invention.

FIG. 5 is a schematic top view showing one example of the package of the present invention.

FIG. 6 is a schematic top view showing one example of the package of the present invention.

FIG. 7 is a schematic top view showing one example of the package of the present invention.

FIG. 8 is a schematic sectional view showing one example of the light emitting device of the present invention.

FIG. 9A is a schematic top view showing one example of the light emitting device of the present invention.

FIG. 9B is a schematic perspective view of one example of the semiconductor device of the present invention.

FIG. 10A is a top view of the ceramics package of this example.

FIG. 10B is a sectional view taken along lines X-X in FIG. 10A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Best modes for carrying out the present invention will now be described below with reference to the accompanying drawings. It should be noted, however, that the forms described below are intended to exemplify the method of manufacturing the support body for semiconductor element and the semiconductor device employing the support body made of ceramics that embody the technical idea of the present invention, and the present invention is not limited to those described below. In some of the accompanying drawings, size and positional relationships are exaggerated in order to make it easier to understand the description. (Method of manufacturing support body for semiconductor element) A support body made of ceramics for mounting a semiconductor element thereon is generally made by using a sheet-form material called the ceramics green sheet. The support body is formed by forming through holes in a stack of ceramics green sheets, forming electrical wirings in the recess wherein the semiconductor element is to be mounted and on the side wall of the through holes and firing the stack. At the time the ceramics green sheets have been stacked, grooves are formed along the centers of the number of through holes. The grooves are formed by firing the stack of ceramic green sheets after incising the ceramics green sheets. The ceramics substrate is separated into individual support bodies by applying a force along the grooves. When the ceramics substrate is separated, the wiring conductor provided in the through hole is exposed on the side face of the support body and is connected to the wiring conductor provided in the recess. Therefore, when the semiconductor element is mounted on the cleavage surface and of the ceramics substrate, namely the side face of the support body, a light emitting device that emits light mainly in the direction substantially parallel to the mounting surface can be made. The support body for semiconductor element in the present invention refers to a member whereon a semiconductor element and the electrical conductor that supplies electric power to the semiconductor element can be mounted, and includes a plate-shaped substrate and the support body that has a recess for mounting a semiconductor element therein, such as ceramics package.

When separating the ceramics substrate into individual support bodies, however, the support body may be broken differently or chipped and the uniform and smooth cleavage surfaces cannot be obtained. As a result, the cleavage surface formed by the conventional manufacturing method results in variability in the optical characteristics of the light source when the light emitting device comprising the semiconductor element mounted on the support body is soldered onto a circuit board. For example, a surface emitting light source is made by combining an optical guide plate wherein light from the light emitting device is caused to enter through an end face of a plate-shaped transparent material and emerge from the other surface through reflections in the transparent material, and a plurality of light emitting devices. At this time, inclination of the light emitting device soldered onto the circuit board differs among the light emitting devices. This difference leads to the angle of incidence of light on the end face of the optical guide plate that is different from the light emitting device to the light emitting device, thus resulting in uneven emission of light from the surface emitting light source and/or variability in the optical characteristics such as optical orientation among the light emitting devices.

In order to solve the problems described above, the inventors of the present application modified the method of manufacturing the support body for semiconductor element whereon the semiconductor element can be mounted, wherein the ceramics substrate is formed by stacking ceramics sheets having electrical conductors provide thereon and cleaving the ceramics substrate along the grooves formed thereon, so as to include a process of separating the ceramics substrate by applying a bending moment and a tensile force to the ceramics substrate. The support body having the electrical conductors exposed on the cleavage surface and in the recess is obtained by cleaving the ceramics substrate along the groove formed on the side wall that constitutes the recess. In other words, the method of manufacturing the substrate for semiconductor element includes at least the following processes.

First, ceramics green sheets not yet fired or ceramics green sheets having through holes are stacked so as to form a stack of unfired ceramics sheets having a recess. Or, alternatively, fired ceramics sheets of flat shape are stacked to form a ceramics substrate.

The predetermined pattern of grooves is formed on the stack of ceramic green sheets for separating the ceramics. For example, the grooves are formed in a matrix of straight line in the longitudinal direction and straight line in the lateral direction. The groove has such a depth that does not affect the mechanical strength of the fired stack of ceramics. The grooves are formed by incising the ceramics green sheets. The incised portions are preferably in a range from ¼ to ¾ of the thickness of the ceramics substrate. The incised portions are more preferably in a range from approximately ⅜ to ⅝ of the thickness of the ceramics substrate. This makes it possible to form the even cleavage surface. This makes possible to improve the productivity in mass production, since this prevents to split off in the carrying step. The incising method can suppress the occurrence of such defect as breakage and chipping of the ceramics substrate than making the groove by polishing. The grooves are preferably formed nor only on the semiconductor element mounting surface but also in the back surface. When making the grooves on back surface, the total depth summed up the depth of the groove on top surface and the depth of the groove on back surface is preferably in a range from ¼ to ¾ of the thickness of the ceramics substrate. Number of the recess surrounded by the grooves formed in the longitudinal direction and lateral direction may be one or more, depending on the number of semiconductor element to be mounted therein. The grooves may also be formed along the center lines of the through holes formed in the stack of ceramic green sheets. This enables it to easily cleave the ceramics substrate that is the fired stack of ceramics sheets. The support body that has been separated with the electrical conductor provided on the inner surface of the through hole being exposed on the cleavage surface can be used to make a sideways emission type light emitting device. The cleavage surface herein includes the inner surface that constitutes the grooves of the ceramics substrate and the surface generated by cleaving the ceramics substrate.

The grooves are formed on the stack of ceramics green sheets in the longitudinal and lateral directions. A through hole is made with the intersect of the longitudinal and lateral grooves located at the center thereof. The through hole is filled with a metallic material that establishes electrical continuity with the electrode provided on the back surface.

The stack of ceramic green sheets is then fired and an electrical wiring and, as required, an optical reflector are formed by plating. The fired stack of ceramic green sheets is cleaved along the grooves, so as to obtain the individual ceramics packages. FIG. 3A through FIG. 3C and FIG. 4A through FIG. 4C are side views schematically showing the processes of separating the ceramics substrate in sequence in the ceramics package manufacturing process of the present invention. There are at least the following forms in the method of manufacturing ceramics package according to the present invention.

Mode 1: Force applying point may be in the direction of extending the depth of the groove on the surface opposite to the surface of the ceramics substrate where the grooves are formed. Specifically, assuming that the groove formed on the principal surface of the fired stack of ceramics sheets is extended in the direction of depth, the intersect of the extended line and the principal surface where the grooves are not formed is used as the point of applying the force. Bending moment can be applied by bringing a cleaving tool to the force applying point.

Which point is used to apply the force has great influence on the ease of cleaving, condition of the cleavage surface and the magnitude of the external force required for cleaving.

Mode 2: A bending moment is applied to the ceramics substrate so that compressive stress is generated on the side where the grooves are formed, and tensile force is generated on the opposite side, bringing the upper ends of the side walls on both sides of the recess into contact with each other. Specifically, as shown in FIG. 4B, bending moment is applied to the fired ceramics substrate so that the upper ends of the side walls on both sides of the recess come into contact with each other. Then as shown in FIG. 4D, bending moment is applied with the contact point of the upper ends of the side walls as the center of moment, while pulling apart the ceramics substrate in the direction parallel to the principal surface, thereby breaking the ceramics substrate. The grooves may also be formed on the surface opposite to the surface having the grooves of the ceramics substrate at a position corresponding to the groove, to the extent that does not affect the mechanical strength of the ceramics substrate.

With the manufacturing method described above, the support body having the predetermined cleavage surface can be made without causing burrs or chippings in the cleavage surface. The support body made of ceramics, particularly a ceramics package having a recess to make a sideways emission type light emitting device can be easily manufactured.

(Semiconductor Device Employing Support Body Made of Ceramics for Semiconductor Element)

FIG. 1A is a schematic top view of the semiconductor device according to this embodiment, and FIG. 2 is a schematic sectional view taken along lines I-I in FIG. 1A. FIG. 1B is a perspective view schematically showing the semiconductor device of the present invention being electrically and mechanically connected by soldering to the mounting surface where the wiring pattern has been formed. As shown in FIG. 1B, the semiconductor device according to this embodiment is a sideways emission type light emitting device that can emit light with optical axis disposed in a direction (Y direction) substantially parallel to the mounting surface 117. FIG. 9A is a schematic top view of the semiconductor device according to another embodiment of the present invention, and FIG. 9B is a schematic sectional view taken along lines IX-IX in FIG. 9A. The semiconductor device 500 shown in FIG. 9 comprises a light emitting element 103 placed on a substrate made of ceramics that is electrically connected to the electrical wiring 105 by an electrical wire 104, while the light emitting element 103 is covered by a sealing member 107. The electric wiring 105 is connected to the electrical wiring 106 exposed on the side face of the substrate, while an electrical circuit is provided on the surface opposite to the light emitting element mounting surface of the ceramics substrate.

The semiconductor device 100 shown in FIG. 1 comprising the support body made of the stack of ceramic sheets having the recess wherein electrical conductor is provided and the semiconductor element electrically connected to the electrical conductor in the recess, wherein at least the top face of the recess side wall is covered by a resin. Specifically, the top face on light emission observing side of the side wall that forms the recess of the ceramics package is covered by a resin over at least a part thereof. A part of the sealing member is extended over the top face of the recess side wall or is impregnated in the side wall of the recess. The top face of the recess side wall covered by the resin can be arranged by screen printing or potting the resin on the top face of the recess side wall, Alternatively, a part of the sealing member that covers at least the light emitting element in the recess of the semiconductor device is extended so as to creep from the recess of the ceramics package over the top face of the recess side wall or is impregnated in the side wall.

The resin or the sealing member preferably includes at least one kind selected from the group of epoxy resin, silicone resin, modified epoxy resin, modified silicone resin, acryl resin or a mixture thereof. This is because the porous ceramics is highly permeable to epoxy resin and silicone resin which can easily be extended over the top face of the recess side wall or is impregnated in the side wall of the recess. A ceramics package that is more porous and is highly permeable to the sealing member can be made by controlling the firing temperature of the ceramics.

When the semiconductor device of this embodiment is used as a sideways emission type light emitting device, solder used in reflow is repelled by the resin that covers the top face of the recess side wall or by the resin that impregnates the side wall of the recess, and is prevented from creeping up to the light emitting plane. Or the solder is repelled by the sealing member extended over the top face of the recess side wall or is impregnated in the side wall of the recess, and cannot creep up to the light emitting plane. This is supposedly because the resin used as the sealing member does not have affinity with the metallic material of the solder. Thus the solder used in reflow is prevented from covering the light emitting surface and does not does have adverse effect on the optical characteristics, and therefore light emitting device of high reliability can be made. When collecting the semiconductor device and an outside circuit board having wiring circuit thereon with solder, such a problem does not occur that solder lines which should be separated as positive and negative polarities in the circuit are brought into contact with each other. As a result, the semiconductor device of high reliability where short-circuiting does not occur can be made.

FIG. 8 is a schematic sectional view of the semiconductor device according to another embodiment of the present invention. The sealing member of this embodiment does not cover the reflecting surface 102 in the recess, while covering at least the semiconductor element 103 and a part of the bottom surface of the recess. When the portion covered by the sealing member is restricted, light emerging from the sealing member is reflected on the reflecting surface 102 and is directed toward the light emitting surface through the air. As a result, undesirable scattering and absorption of light by an excessive sealing member is minimized and optical output of the light emitting device can be improved.

The resin of this embodiment also covers the top face of the recess side wall as indicated by Y in the enlarged sectional view of FIG. 8. Electrically conductive reflecting surface 102 is provided on the inner wall surface that forms the recess of the ceramics package, so as to make the light emitting device wherein the sealing member 107 does not cover the reflecting surface 102 such as the light emitting device of another embodiment shown in FIG. 8. In this case, solder may creep up to the reflecting surface 102 during the reflow. Moreover, short-circuiting may occur as solder lines which should be separated as positive and negative polarities in the circuit are brought into contact with the reflecting surface 102.

In the light emitting device of another embodiment, since creeping up of the solder is prevented by the resin that covers the top face of the recess side wall, the solder never touches the reflecting surface during the reflow. As a result, covering of the light emitting surface by the solder is suppressed and adverse effect on the optical characteristics is eliminated. Now the constitution of this embodiment will be described below.

[Ceramics Package]

The ceramics package manufactured according to the present invention is made of a ceramics material to protect the semiconductor element from the environment. The ceramics package is an example of the support body for semiconductor element whereon the semiconductor element is mounted in the recess and members are provided for electrical connection with the outside. The ceramics material is preferably alumina, aluminum nitride, mulite or the like. Particularly, a ceramics material consisting of 90 to 96% by weight of alumina and 4 to 10% by weight of a sintering agent such as clay, talc, magnesia, calcia, silica or the like that is sintered at a temperature from 1500 to 1700° C., or a ceramics material consisting of 40 to 60% by weight of alumina and 60 to 40% by weight of a sintering agent such as borosilicate glass, cordierite, foresterite, mulite or the like that is sintered at a temperature from 800 to 1200° C.

Such a ceramics package can be formed in various shapes in the stage of green sheets before firing. The wiring conductor in the package is made of a paste material comprising a resin binder containing high melting point metal such as tungsten and molybdenum. The paste material is formed in a desired shape via the through hole provided in the green sheet by screen printing, and is turned into the wiring conductor by firing. By stacking the green sheets having the through hole in multi-layer structure, the recess to mount the semiconductor element therein is formed. Therefore, recesses of various shapes can be formed by stacking green sheets having through holes of circular or oval shape and/or having different sizes when viewed from the light emission observing side. Moreover, a recess of which inner diameter increases toward the mouth can be formed by combining green sheets having through holes of which inner diameter increases in a particular direction and green sheets having through holes of different shapes and sizes. The green sheets having through holes of which inner diameter increases in a particular direction can be made by using a cutting tool of which cutting edge becomes narrower in the direction of contact with the green sheet. Alternatively, green sheets may be formed by changing the angle of contact of the cutting tool, used in forming the ordinary through holes, with the green sheet. Furthermore, green sheets having through holes of which inner diameter increases in a particular direction can be made by stacking a plurality of green sheets having through holes with inner diameter varied stepwise so as to form a stepped inner wall surface and pressing a molding die against the stepped inner wall surface.

The ceramics package is made by stacking the green sheets and sintering the stack. A dark color can also be obtained by containing Cr₂O₃, MnO₂, TiO₂ or Fe₂O₃in the green sheet.

The recess of the package is for mounting the semiconductor element and/or the electrically conductive wire therein. Therefore, size of the recess may be such that the semiconductor element mounted therein by die bonding or the like, and electrical connection with the semiconductor element can be made by wire bonding. The semiconductor element can be bonded onto the bottom of the package, for example, by means of a thermosetting resin. Specifically, epoxy resin, acrylic resin or imide resin may be used. In case flip chip mounting is employed by directly connecting the electrodes of the semiconductor element and the wiring conductor provided in the recess disposed to oppose each other, Ag paste, ITO paste, carbon paste, metal bump or the like may be sued to electrically connect the wiring conductor. The semiconductor element may be bonded onto the exposed ceramics material via an insulating adhesive. With this constitution, the semiconductor element can be secured more firmly on the ceramics package compared to a case where it is bonded onto the wiring conductor by means of an insulating adhesive.

[Reflecting Surface]

When the ceramics package is used as the light emitting device that uses a light emitting element as the semiconductor element, a light reflecting surface can be formed in a part of the inner surface of the recess. Since ceramics generally transmits light, efficiency of the light emitting device to extract light can be improved by forming the reflecting surface so as to reflect the light from the light emitting element toward the light emission observing side. The reflecting surface 102 is provided for a part of the inner surface of the recess in the principal surface of the ceramics package, and includes a first metal layer that makes direct contact with the ceramics base material of the ceramics package and serves as the base for a second metal layer, and the second metal layer reflects the light emitted by the light emitting element so as to efficiently extract the light to the outside. Now the first metal layer and the second metal layer will be described in detail below. The reflecting surface of this embodiment can also serve as the electrical conductor for supplying the power to the semiconductor element in the process of forming the ceramics package.

(First Metal Layer)

The first metal layer is formed to as to make direct contact with the support body made of ceramics and serves as the base for a second metal layer. As such, the first metal layer that is formed when firing the ceramics must not melt when forming the ceramics. Metals having such a high melting point suitable for the first metal layer include tungsten, chromium, titanium, cobalt, molybdenum and alloys thereof. The first metal layer can be formed by mixing particles of such a metal in a resin paste, applying the paste to the inner surface of the recess of a green sheet by coating or printing and firing the green sheet. Bonding of the second metal layer formed on the ceramics and the first metal layer, and bonding of the sealing member formed on the second metal layer can be controlled by controlling the particle size of the metal. By controlling the particle size of the metal used in the first metal layer, surface roughness of the second metal layer formed thereon can be controlled. Thus the particle size of the metal used in the first metal layer is preferably in a range from 0.3 to 100 μm, and more preferably from 1 to 20 μm.

Instead of screen printing on the inner surface, the reflecting surface can also be formed by filling up the opening of the green sheet with an electrically conductive paste and then drilling at the center of the opening with laser beam leaving an electrically conductive layer on the inner wall. Carbon dioxide gas laser, YAG laser, excimer layer or the like may be used as the laser. The first metal layer may not necessarily be formed over the entire surface of the inner wall. Light can be reflected only in a desired direction by leaving a portion where the first metal layer and the second metal layer are not formed. Light can be seen as diffusing through the ceramics in the portion where the metal layer is not formed. The view angle can be increased by forming the metal layer partially on the inner wall. The first metal layer that constitutes the reflecting surface can be formed by applying a resin paste, containing a high melting point metal that constitutes the wiring conductor, onto the inner wall.

(Second Metal Layer)

The second metal layer is formed on the first metal layer, to serve as a reflector for efficiently extracting the light emitted by the light emitting element to the outside. The second metal layer can be formed on the first metal layer relatively easily by plating or vapor deposition. The second metal layer may be made of a metal that has 90% or higher reflectivity to the light emitted by an LED chip such as gold, silver, platinum, aluminum, nickel, palladium or an alloy thereof, or a multi-layer film made of such metals.

The second metal layer may also be formed at the same time as surface treatment is applied to the wiring pattern formed in the ceramics package. That is, Ni/Ag or Ni/Au may be plated on the electrical wiring provided in the ceramics package at the same time as the metal layer is formed, in order to improve the solderability. The second metal layer and the electrical wiring may also be formed by plating separately. Loss of light below the light emitting element can be suppressed by covering the electrical wiring provided at the bottom of the recess with the second metal layer.

[Semiconductor Element]

The support body made of ceramics can support a light emitting element (may also be called the LED chip in this specification), a light receiving element and a protective element that protects the functional elements from breakage due to over voltage, mounted thereon in combination or separately. Although this embodiment deals with a case where a light emitting element is used as the semiconductor element, it needs not to say that the semiconductor element of the present invention is not limited to light emitting element.

(Light Emitting Element)

As the light emitting element that can be mounted on the support body made of ceramics, such elements having a light emitting layer made of GaAlN, ZnS, ZnSe, SiC, GaP, GaAlAs, AlN, InN, AlInGaP, InGaN, GaN, AlInGaN or other semiconductor formed on a substrate may be used. Preferable structures of the light emitting element include homojunction structure, heterojunction structure or double heterojunction structure that has MIS junction, PIN junction or PN junction. Emission wavelength can be controlled over a broad range from ultraviolet to infrared regions by selecting the semiconductor material and adjusting the composition of mixed crystal. The light emitting layer may formed in a thin film where quantum effect can be utilized having single quantum well structure or multiple quantum well structure.

Gallium nitride semiconductor is preferably used as a semiconductor material that can form a light emitting element having high luminance. To emit red light, a semiconductor based on gallium, aluminum and arsenic, or a semiconductor based on aluminum, indium, gallium and phosphorus is preferably used, but it needs not to say that various semiconductors may be used depending on the application.

When a gallium nitride semiconductor is used, the substrate can be made of sapphire, spinel, SiC, Si, ZnO, GaAs, GaN single crystal or the like. In order to form the gallium nitride semiconductor with good crystallinity and characteristic suitable for mass production, it is preferable to use a sapphire substrate. An example of LED chip formed from nitride semiconductor will be described below. A buffer layer is formed from GaN, AlN or the like on the sapphire substrate. On the buffer layer, a first contact layer made of GaN having N or P type, an active layer made of thin InGaN film that has quantum effect, a cladding layer made of AlGaN having P or N type and a second contact layer made of GaN having P or N type are formed in this order. Gallium nitride semiconductor has N-type electrical conductivity when not doped with an impurity. It is preferable that Si, Ge, Se, Te, C or the like is introduced as an n-type dopant if an N-type gallium nitride semiconductor having desired characteristics such as the efficiency of light emission is to be formed.

When a P-type gallium nitride semiconductor is to be formed, on the other hand, Zn, Mg, Be, Ca, Sr, Ba or the like is added as a P-type dopant. Since a gallium nitride semiconductor is difficult to turn into P-type simply by doping with a P-type dopant, it is necessary to anneal the semiconductor by heating in a furnace or irradiating with plasma after the introduction of the P-type dopant. A positive electrode and a negative electrode are formed by partially etching the semiconductor wafer thus formed. Then after forming the electrodes on both contact layers, the wafer is diced into chips thereby by making the LED chips.

The light emitting element can be used in plurality, and through proper selection of the combination thereof, color blending performance can be improved when providing white light emission. For example, two light emitting elements capable of emitting greenish light and one each light emitting element capable of emitting bluish light and reddish light may be combined. In order to make a full-color light emitting device for a display apparatus, it is preferable to combine such emission spectra as wavelengths from 610 to 700 nm for red, wavelength from 495 to 565 nm for green and wavelengths from 430 to 490 nm for blue. In order make a light emitting device that emits white light by color blending, it is preferable to use the light emitting element that emits light of wavelengths from 400 nm to 530 nm, more preferably from 420 nm to 490 nm, in consideration of the complementary color relationship with the light emitted by the fluorescent material, deterioration of the translucent resin and other factors. In order to improve the efficiency of excitation and light emission of the fluorescent material, the emission wavelengths are more preferably in a range from 450 to 475 nm. A light emitting element that has principal emission wavelength in the ultraviolet region of wavelength shorter than 400 nm or in a short wavelength region of the visible light may also be used by combining with a member that is less likely to be deteriorated by ultraviolet ways.

(Protective Element)

As the protective element, a zener diode that turns to conductive state when a voltage higher than a threshold is applied, a capacitor that absorbs voltage surge may be used.

The zener diode is constituted from a p-type semiconductor region having a positive electrode and an n-type semiconductor region having a negative electrode, and is connected in reverse parallel connection with the p-type electrode and the n-type electrode of the light emitting element. In other words, the n-type electrode and the p-type electrode of the light emitting element are connected to the electrodes of the p-type semiconductor region and the n-type semiconductor region of the zener diode, respectively. Moreover, a zener diode may also be used for sub-mount where the light emitting element is provided by flip-chip mounting via bump. At this time, the n-type electrode and the p-type electrode of the light emitting element are mechanically and electrically connected to the electrodes of the p-type semiconductor region and the n-type semiconductor region of the zener diode that is exposed on the surface of the sub-mount, respectively. The positive and negative electrodes provided on the sub-mount serving as the zener diode can be connected to the electrical wiring by the electrically conductive wires. When the sub-mount is caused to serve as the zener diode, as described above, voltage across the positive and negative electrodes of the light emitting element is latched at the zener voltage and never increases above the zener voltage even if a voltage above the zener voltage is applied across the positive and negative electrodes of the light emitting element. Thus an excessive voltage is prevented from being applied to the light emitting element so as to protect the light emitting element from over voltage and prevent destruction and deterioration of the element.

For the capacitor used as a protective element, a surface-mounted chip component may be used. A capacitor of this type has electrodes formed in band-shape on both sides, with these electrodes connected in parallel to the positive and negative electrodes of the light emitting element. When an over voltage is applied across the positive and negative leads of the capacitor, a charging current flow in the capacitor so as to reduce the voltage across the capacitor terminals, so that the over voltage is not applied to the light emitting element thereby protecting the light emitting element from the over voltage. When noise that includes high frequency components is applied, too, the capacitor functions as a bypass capacitor and shuts off the noise.

[Sealing Member 107]

The sealing member is provided to cover the LED chip to protect the LED chip from forces and moisture coming from the outer environment and emit the light from the LED chip efficiently to the outside. The sealing member may be made of a transparent material that has high weatherability such as epoxy resin, urea resin and silicone resin, light-permeable inorganic material that is produced from metal alkoxide as the starting material by sol-gel process, glass or the like. The resin and the sealing member of this embodiment are preferably made of a transparent resin that has high permeability to ceramics.

In case the LED chips are packaged with high density, it is more preferable to use epoxy resin, silicone resin, modified epoxy resin, modified silicone resin or a mixture thereof in consideration of such troubles as breakage of electrically conductive wires due to thermal shock. The sealing member may also include diffusion agent in order to increase the view angle. For the diffusion agent, barium titanate, titanium oxide, aluminum oxide, silicon oxide or a mixture thereof can be preferably used. An organic or inorganic dye or pigment may also be included in order to cut off undesirable wavelengths. A fluorescent material that converts the wavelength of at least a part of light emitted by the LED chip may also be included.

[Fluorescent Material]

The fluorescent material used in the present invention absorbs a part of visible light or ultraviolet ray emitted by the light emitting element, and emits light of wavelength different from that of the absorbed light. The fluorescent material is, besides being included in the sealing member described above, included in the coating member provided to cover the LED chip, the insulating adhesive (or example, epoxy resin, silicone resin or a transparent inorganic material such as glass) used for securing the LED chip on the package and in the ceramics package (particularly the portion not covered by the reflecting surface). The fluorescent material may be, besides covering the surface of the sealing member, provided as a layer or a sheet containing the fluorescent material at a position spaced from the surface of the sealing member or from the light emitting element.

The fluorescent material is such that is excited at least by the light emitted by the semiconductor light emitting layer of the LED chip and emits light of converted wavelength, and is combined with a binding agent that secures the fluorescent material to form a wavelength converting member.

In case the light emitted by the LED chip and the light emitted by the fluorescent material are in the relationship of complementary colors, white light can be generated by blending both light. Specifically, there are such cases as the light emitted by the LED chip and the light emitted by the fluorescent material that is excited by the former are the primary colors of light (red, green and blue), or blue light emitted by the LED chip and yellow light emitted by the fluorescent material that is excited by the former are used.

Color of the light emitted by the light emitting device can be controlled so as to generate white light of various color tones including that of incandescent lamp by adjusting the proportions of various kinds of resin and inorganic material such as glass that serve as the binding agents between fluorescent materials, sedimentation time of the fluorescent material and the shape of the fluorescent material, and selecting the emission wavelength of the LED chip. It is preferable that the light emitted by the LED chip and the light emitted by the fluorescent material transit efficiently through the sealing member from the light emission observing side of the light emitting device.

Since the fluorescent material in gas phase or liquid phase sediments by the gravity, a layer having the fluorescent material more uniformly distributed can be formed by dispersing the florescent material in gas phase or liquid phase. A desired fluorescent material layer can be formed by repeating the process a plurality of times.

The fluorescent material formed as described above may be provided either in a plurality of kinds in the wavelength converting member constituted from a single layer on the surface of the light emitting device, or in a single kind or a plurality of kinds in the wavelength converting member constituted from two layers. This constitution makes it possible to obtain white light through blending of the light emitted by different fluorescent materials. In this case, it is preferable that the fluorescent materials have similar mean particle sizes and shapes in order to achieve satisfactory blending of the light emitted by the different fluorescent materials and minimize color unevenness. Particle size of the fluorescent material in the present invention is a value determined from volumetric particle size distribution curve. The volumetric particle size distribution curve is determined from the measurement of particle size distribution by the laser diffraction and diffusion method. Specifically, the fluorescent material is dispersed in 0.05% aqueous solution of sodium hexa-metaphosphate at temperature of 25 and humidity of 70%, and measuring with a laser diffraction particle size distribution measuring instrument (SALD-2000A) in a range from 0.03 to 700 um.

In this embodiment, a fluorescent material made by combining aluminum garnet fluorescent material represented by YAG fluorescent material and a fluorescent material capable of emitting red light, particularly a nitride fluorescent material, can be used. The YAG fluorescent material and the nitride fluorescent material may be either mixed and included in the wavelength converting member or included separately in different wavelength converting members formed in a plurality of layers. The different fluorescent materials will now be described below.

(Aluminum Garnet Fluorescent Material)

Aluminum garnet fluorescent material is a fluorescent material that contains Al, at least one element selected from among Y, Lu, Sc, La, Gd, Tb, Eu, Ga, In and Sm, and at least one element selected from among Ga and In and is activated with at least one element selected from among the rare earth elements, and is excited by visible light or ultraviolet ray emitted by the LED chip so as to emit light. Besides the YAG fluorescent material described above, Tb_(2.95)Ce_(0.05)Al₅O₁₂, Y_(2.90)Ce_(0.05)Tb_(0.05)Al₅O₁₂, Y_(2.94)Ce_(0.05)Pr_(0.01)Al₅O₁₂, Y_(2.90)Ce_(0.05)Pr_(0.05)Al₅O₁₂ may be used. Among these, yttrium aluminum oxide fluorescent material of two or more kinds having different compositions that include Y and are activated with Ce or Pr are particularly preferably used in this embodiment.

Specifically, yttrium aluminum garnet fluorescent material (may be hereinafter called the YAG fluorescent material) activated with cerium may be used. For use with high luminance over a long period of time, in particular, (Re_(1-x)Sm_(x))₃(Al_(1-y)Ga_(y))₅O₁₂: Ce (0≦x≦1, 0≦y≦1, where Re represents at least one kind of element selected from among Y, Gd and La) or the like is preferably used.

The (Re_(1-x)Sm_(x))₃(Al_(1-y)Ga_(y))₅O₁₂: Ce fluorescent material is durable against heat, light and moisture, because of the garnet structure. It also allows it to set the peak wavelength of excitation spectrum at around 470 nm. A broad emission spectrum that has emission peak around 530 nm and tails off to 720 nm can be obtained.

RGB components can be increased by mixing two or more kinds of (Re_(1-x)Sm_(x))₃(Al_(1-y)Ga_(y))₅O₁₂:Ce fluorescent material having different contents of Al, Ga, In, Y, La, Gd and Sm for the YAG fluorescent material. While some semiconductor light emitting element are subject to variations in the emission wavelength, blended light of desired white-based color can be obtained by mixing two or more kinds of fluorescent material. Specifically, by combining the fluorescent materials having different values of chromaticity to match the emission wavelength of the light emitting element, light of desired chromaticity can be emitted at any point on the chromaticity diagram in a region defined by the points corresponding to the fluorescent materials and the light emitting element.

White light of desired color tone can be emitted by blending blue light emitted by a light emitting element that employs a nitride semiconductor in the light emitting layer, green light emitted by a fluorescent material having yellow body color for absorbing blue light and, as required, red light. In order to perform this color blending in the light emitting device, fluorescent material in powder or bulk form may be included in various resins such as epoxy resin, acrylic resin or silicone resin, and light-permeable inorganic material such as silicon oxide or aluminum oxide. Such a material that includes the fluorescent material can be used in various forms such as dots or layer as thin as permeable to the light emitted by the LED chip, depending on the application. Light of desired color tones including that of incandescent lamp may be produced by adjusting the proportions of the fluorescent material and inorganic material and the quantity used in coating or filling.

Use of YAG fluorescent material enables it to make a light emitting device having high efficiency and resistance to light even when disposed adjacent or in proximity to an LED chip having illuminance of radiation in a range from (Ee)=0.1 W·cm⁻² to 1000 W·cm⁻².

Yttrium aluminum oxide fluorescent material activated with cerium, that is a fluorescent material capable of emitting light in green region, is durable against heat, light and moisture because of the garnet structure and has peak wavelength of excitation spectrum in a range from 420 nm to 470 nm. It also has peak emission wavelength λp around 510 nm and has a broad emission spectrum that tails off to around 700 nm. Yttrium aluminum oxide fluorescent material activated with cerium, that is a fluorescent material capable of emitting light in red region also as garnet structure and, is durable against heat, light and moisture and has peak wavelength of excitation spectrum in a range from 420 nm to 470 nm. It also has peak emission wavelength λp around 600 nm and has a broad emission spectrum that tails off to around 750 nm.

Emission spectrum of the YAG fluorescent material having garnet structure shifts toward shorter wavelengths when part of Al in the composition thereof is substituted by Ga, and shifts toward longer wavelengths when part of Y is substituted by Gd and/or La. In this way the color of emitted light can be changed continuously by changing the composition. As a result, the fluorescent material has the ideal feature for converting the light in blue region emitted by the nitride semiconductor into white light, including continuously changing the intensity of light of longer wavelength by changing the proportion of Gd. When less than 20% of Y is substituted, green component increases and red component decreases, while red component increases but luminance shows marked decrease when 80% or more of Y is substituted. The excitation spectrum, too, of the YAG fluorescent material having garnet structure shifts toward shorter wavelengths when part of Al is substituted by Ga, and shifts toward longer wavelengths when part of Y is substituted by Gd and/or La. Peak emission wavelength of the excitation spectrum of the fluorescent material is preferably shorter than the peak wavelength of the emission spectrum of the light emitting element. With this constitution, since the peak wavelength of the excitation spectrum substantially agrees with the peak wavelength of the emission spectrum of the light emitting element, color deviation can be prevented from occurring without decreasing the excitation efficiency of the fluorescent material, when the current supply to the light emitting element is increased.

Stock material for the fluorescent material is made by mixing oxides of Y, Gd, Ce, La, Al, Sm, Pr, Tb and Ga or compounds that can be easily turned into such oxides at a high temperature are well mixed in stoichiometrical proportions. Alternatively, a solution of a mixture of rare earth elements Y, Gd, Ce, La, Al, Sm, Pr, Tb in stoichiometrical proportions dissolved in an acid is coprecipitated with oxalic acid, of which product is fired to obtain a coprecipitated oxide which is mixed with aluminum oxide and gallium oxide to obtain a stock material mixture. This mixture, with a fluoride such as ammonium fluoride added thereto as a flux, is put into a crucible and fired at a temperature from 1350 to 1450 in air for two to five hours. The fired mixture is crushed in a ball mill in wet process, and undergoes the processes of washing, separation, drying and sieving. In a method of manufacturing the fluorescent material according to another embodiment, the mixture of the stock materials of the fluorescent material and the flux is fired preferably in two stages: a first firing process carried out in the air or in weakly reducing atmosphere, and a second firing process carried out in reducing atmosphere. The weakly reducing atmosphere means an atmosphere having weak reducing power that is controlled to include at least such a concentration of oxygen that is required in the reaction to form the desired fluorescent material from the mixed material. The first firing process carried out in the weakly reducing atmosphere till the formation of the fluorescent material of desired composition is completed makes it possible to prevent the fluorescent material from blackening and the light absorbing efficiency from decreasing. The reducing atmosphere of the second firing process refers to a reducing atmosphere that has higher reducing power than the weakly reducing atmosphere. A fluorescent material having higher absorption efficiency at the excitation wavelength can be made by firing in two stages as described above. In consequence, when the light emitting device is made by using the fluorescent material obtained as described above, quantity of the fluorescent material required to obtain the desired color tone can be reduced and the efficiency of extracting light can be increased.

Two or more kinds of yttrium aluminum oxide fluorescent materials of different compositions activated with cerium may be either mixed with each other or disposed separately. When the fluorescent materials of different compositions are disposed separately, it is preferable to dispose the fluorescent material that absorbs light of shorter wavelength nearer to the light emitting element and the fluorescent material that absorbs light of longer wavelength next to it. This arrangement achieves efficient absorption and emission. (Nitride fluorescent material) The fluorescent material of this embodiment may be a nitride fluorescent material that contains N, at least one element selected from among Be, Mg, Ca, Sr, Ba and Zn, and at least one element selected from among C, Si, Ge, Sn, Ti, Zr, and Hf and is activated with at least one element selected from among the rare earth elements. The nitride fluorescent material used in this embodiment is a fluorescent material that absorbs visible light or ultraviolet ray emitted by the LED chip or light emitted by the YAG fluorescent material so as to be excited and emit light. There can be manufactured fluorescent materials based on various combinations, for example, Ca—Ge—N: Eu,Z, Sr—Ge—N: Eu,Z, Sr—Ca—Ge—N: Eu,Z, Ca—Ge—O—N: Eu,Z, Sr—Ge—O—N: Eu,Z, Sr—Ca—Ge—O—N: Eu,Z, Ba—Si—N: Eu,Z, Sr—Ba—Si—N: Eu,Z, Ba—Si—O—N: Eu,Z, Sr—Ba—Si—O—N: Eu,Z, Ca—Si—C—N: Eu,Z, Sr—Si—C—N: Eu,Z, Sr—Ca—Si—C—N: Eu,Z, Ca—Si—C—O—N: Eu,Z, Sr—Si—C—O—N: Eu,Z, Sr—Ca—Si—C—O—N: Eu,Z, Mg—Si—N: Eu,Z, Mg—Ca—Sr—Si—N: Eu,Z, Sr—Mg—Si—N: Eu,Z, Mg—Si—O—N: Eu,Z, Mg—Ca—Sr—Si—O—N: Eu,Z, Sr—Mg—Si—O—N: Eu,Z, Ca—Zn—Si—C—N: Eu,Z, Sr—Zn—Si—C—N: Eu,Z, Sr—Ca—Zn—Si—C—N: Eu,Z, Ca—Zn—Si—C—O—N: Eu,Z, Sr—Zn—Si—C—O—N: Eu,Z, Sr—Ca—Zn—Si—C—O—N: Eu,Z, Mg—Zn—Si—N: Eu,Z, Mg—Ca—Zn—Sr—Si—N: Eu,Z, Sr—Zn—Mg—Si—N: Eu,Z, Mg—Zn—Si—O—N: Eu,Z, Mg—Ca—Zn—Sr—Si—O—N: Eu,Z, Sr—Mg—Zn—Si—O—N: Eu,Z, Ca—Zn—Si—Sn—C—N: Eu,Z, Sr—Zn—Si—Sn—C—N: Eu,Z, Sr—Ca—Zn—Si—Sn—C—N: Eu,Z, Ca—Zn—Si—Sn—C—O—N: Eu,Z, Sr—Zn—Si—Sn—C—O—N: Eu,Z, Sr—Ca—Zn—Si—Sn—C—O—N: Eu,Z, Mg—Zn—Si—Sn—N: Eu,Z, Mg—Ca—Zn—Sr—Si—Sn—N: Eu,Z, Sr—Zn—Mg—Si—Sn—N: Eu,Z, Mg—Zn—Si—Sn—O—N: Eu,Z, Mg—Ca—Zn—Sr—Si—Sn—O—N: Eu,Z and Sr—Mg—Zn—Si—Sn—O—N: Eu,Z. Z that represents rare earth element preferably contains at least one kind selected from among Y, La, Ce, Pr, Nd, Tb, Dy, Ho, Er and Lu, but may also include Sc, Sm, Tm, Yb. These rare earth elements are mixed in the material either in the form of simple substance or compounds such as oxide, imide or amide. While rare earth elements have trivalent electron configuration, Yb, Sm and the like have divalent electron configuration and Ce, Pr, Tb and the like have quadrivalent electron configuration. When a rare earth element is used in the form of oxide, presence of oxygen affects the light emission characteristics of the fluorescent material. In other words, presence of oxygen may cause a decrease in the luminance of emitted light, although it provides an advantage of reducing the duration of afterglow. Inclusion of Mn, on the other hand, increases the particle size and improves the luminance of emitted light.

For example, La is used as a co—activation agent. Lanthanum oxide (La₂O₃) is a white crystalline material, which quickly turns into carbonate when left in air and is therefore kept in inert gas atmosphere.

For example, Pr is used as a co-activation agent. Praseodymium oxide (Pr₆O₁₁) is a non-stoichiometrical compound, unlike ordinary oxides of rare earth elements Z₂O₃.

When oxalate, hydroxide, carbonate or other compound of praseodymium is heated to 800° C. in air, a black powder having composition of Pr₆O₁₁ is obtained. Pr₆O₁₁, that is used as the starting material for synthesizing a praseodymium compound, is commercially available with high purity.

The fluorescent material is a silicon nitride based on Sr—Ca—Si—N: Eu, Ca—Si—N: Eu, Sr—Si—N: Eu, Sr—Ca—Si—O—N: Eu, Ca—Si—O—N: Eu or Sr—Si—O—N: Eu containing Mn added thereto. Basic composition of this fluorescent material is represented by general formula L_(X)Si_(Y)N_((2/3X+4/3Y)):Eu or L_(X)Si_(Y)O_(Z)N_((2/3X+4/3Y-2/3Z)) :Eu (L is one selected from among Sr, Ca and Sr plus Ca) Values of X and Y in the formula are preferably X=2 and Y=5 or X=1 and Y=7, but may be various other values. Specifically, fluorescent material having basic compositions (Sr_(X)Ca_(1-x))₂Si₅N₈: Eu, Sr₂Si₅N₈: Eu, Ca₂Si₅N₈: Eu, Sr_(X)Ca_(1-x)Si₇N₁₀: Eu, SrSi₇N₁₀: Eu or CaSi₇N₁₀: Eu containing Mn added thereto is preferably used. The fluorescent materials having basic compositions may include at least one element selected from among a group consisting of Mg, Sr, Ca, Ba, Zn, B, Al, Cu, Mn, Cr and Ni. The present invention is not limited to this embodiment and example. L is one selected from among Sr, Ca and Sr plus Ca. Proportions of Sr and Ca may be changed as required. A fluorescent material of low cost and good crystallinity can be made by containing Si in the composition.

Europium Eu which is a rare earth element is used as the luminescence center. Europium has main energy levels, divalent and trivalent. Eu²⁺ is used as the activation agent for the fluorescent material based on alkaline earth metal silicon nitrate. Eu²⁺ is easily oxidized and is commercialized in the trivalent form of Eu₂O₃. But when the commercially available Eu₂O₃ is used, significant participation of O in the reaction makes it difficult to obtain a satisfactory fluorescent material. Therefore, it is preferable to remove O from Eu₂O₃. For examples, it is preferable to use simple substance of europium or europium nitride. This does not apply when Mn is added.

Examples of the fluorescent material which can be manufactured include, but are not limited to, Sr₂Si₅N₈: Eu,Pr, Ba₂Si₅N₈: Eu,Pr, Mg₂Si₅N₈: Eu,Pr, Zn₂Si₅N₈: Eu,Pr, SrSi₇N₁₀: Eu,Pr, BaSi₇N₁₀: Eu,Ce, MgSi₇N₁₀: Eu,Ce, ZnSi₇N₁₀: Eu,Ce, Sr₂Ge₅N₈: Eu,Ce, Ba₂Ge₅N₁₀: Eu,Pr, Mg₂Ge₅N₈: Eu,Pr, Zn₂Ge₅N₈: Eu, Pr, SrGe₇N₁₀: Eu, Ce, BaGe₇N₁₀: Eu, Pr, MgGe₇N₁O: Eu, Pr, ZnGe₇N₁₀: Eu,Ce, Sr_(1.8)Ca_(0.2)Si₅N₈: Eu,Pr, Ba_(1.8)Ca_(0.2)Si₅N₈: Eu,Ce, Mg_(1.8)Ca_(0.2)Si₅N₈: Eu,Pr, Zn_(1.8)Ca_(0.2)Si₅N₈: Eu,Ce, Sr_(0.8)Cao₂Si₇N₁₀: Eu,La, Ba_(0.8)BCa_(0.2)Si₇N₁₀: Eu,La, Mg_(0.8)Ca_(0.2)Si₇N₁₀: Eu,Nd, Zn_(0.8)Ca_(0.2)Si₇N₁₀: Eu,Nd, Sr_(0.8)Ca_(0.2)Ge₇N₁₀: Eu,Tb, Ba_(0.8)Ca_(0.2)Ge₇N₁₀: Eu,Tb, Mg_(0.8)Ca_(0.2)Ge₇N₁₀: Eu,Pr, Zn_(0.8)Ca_(0.2)Ge₇N₁₀: Eu,Pr, Sr_(0.8)Ca_(0.2)Si₆GeN₁₀: Eu,Pr, Ba_(0.8)Ca_(0.2)Si₆GeN₁₀: Eu,Pr, Mg_(0.8)Ca_(0.2)Si₆GeN₁₀: Eu,Y, Zn_(0.8)Ca_(0.2)Si₆GeN₁₀: Eu,Y, Sr₂Si₅N₈: Pr, Ba₂Si₅N₈: Pr, Sr₂Si₅N₈: Tb, BaGe₇N₁₀: Ce.

Addition of Mn accelerates the diffusion of Eu²⁺, and improves luminance of light emission, energy efficiency and the efficiency of light emission such as quantum efficiency. Mn is either mixed in the stock material or supplied in the form of simple substance of Mn or Mn compound in the manufacturing process and fired together with the stock material. The fired material does not include Mn or, if it does, only a small fraction of that which was added. This is supposedly because Mn was dissipated during the firing process.

The fluorescent material contains at least one element selected from among a group consisting of Mg, Ga, In, Li, Na, K, Re, Mo, Fe, Sr, Ca, Ba, Zn, B, Al, Cu, Mn, Cr, O and Ni in the basic composition or in addition to the basic composition. These elements have such effects as increasing the particle size and increasing the luminance of light emission. B, Al, Mg, Cr and Ni have the effect of suppressing afterglow.

The nitride fluorescent material described above absorbs a part of blue light emitted by the LED chip and emits light in yellow to red region. Thus the present invention provides a light emitting device that uses the nitride fluorescent material and the YAG fluorescent material and emits blended white light of warm color tone by blending blue light emitted by the LED and the light of yellow to red color emitted by the nitride fluorescent material. In addition to the nitride fluorescent material, yttrium aluminum oxide fluorescent material activated with cerium is preferably included. Light color can be adjusted to desired chromaticity when yttrium aluminum oxide fluorescent material is included. The yttrium aluminum oxide fluorescent material activated with cerium absorbs a part of blue light emitted by the LED chip and emits yellow light. The blue light emitted by the LED chip and the yellow light emitted by the yttrium aluminum oxide fluorescent material are blended to produce bluish white light. Therefore, when the yttrium aluminum oxide fluorescent material and a fluorescent material that emits red light are mixed and included in the transparent coating material and the blue light emitted by the LED chip is combined therewith, a light emitting device capable of emitting white light can be provided. Particularly preferable is a light emitting device that emits white light having chromaticity curve of a black body on the chromaticity diagram. However, quantities of the yttrium aluminum oxide fluorescent material and the fluorescent material that emits red light may be changed to provide a light emitting device that emits light of desired color temperature. The light emitting device that emits white light by blending is intended to improve the special color rendering index R9. The conventional light emitting device that emits white light by simply combining a blue light emitting diode and a yttrium aluminum oxide fluorescent material activated with cerium has special color rendering index R9 that is almost 0 around color temperature Tcp=4600 K, and lacks red component, thus giving rise to a demand for means to improve the special color rendering index R9. The present invention makes it possible to improve the value of special color rendering index R9 to about 40 around color temperature Tcp=4600 K by using the fluorescent material that emits red light along with the yttrium aluminum oxide fluorescent material.

Now the method of manufacturing (Sr_(x)Ca_(1-x))₂Si₅N₈:Eu according to the present invention will be described below. It is understood that the present invention is not limited to this manufacturing method. The fluorescent material described above contains Mn and O.

First, stock materials Sr and Ca are crushed. While Sr and Ca are preferably supplied in the form of simple substance, compounds such as imide compound or amide compound may also be used. The stock materials Sr and Ca may include B, Al, Cu, Mg, Mn, MnO, Mn₂O₃, or Al₂O₃. The stock materials Sr and Ca are crushed in a glove box in argon atmosphere. Mean particle size of crushed Sr and Ca is preferably in a range from about 0.1 μm to 15 μm, but is not limited to this range. Purity of Sr and Ca is preferably 2N or higher, but is not limited to this level. In order to better mix the materials, at least one of metal Ca, metal Sr and metal Eu may be alloyed and used as the stock material after nitriding and crushing.

Stock material Si is crushed. While Si is preferably supplied in the form of simple substance, compounds such as nitride, imide compound or amide compound may also be used, for example, Si₃N₄, Si(NH₂)₂ or Mg₂Si. Purity of the stock material Si is preferably 3N or higher, but such compounds may be included as Al₂O₃, Mg, metal borate (CO₃B, Ni₃B, CrB), manganese oxide, H₂BO₃, B₂O₃, Cu₂O and CuO. Similarly to the stock materials Sr and Ca, is also crushed in a glove box in argon atmosphere or nitrogen atmosphere. Mean particle size of the Si compound is preferably in a range from about 0.1 um to 15 um.

The stock materials Sr and Ca are nitrided in nitrogen atmosphere. This reaction is represented by the following schemes 1 and 2. 3Sr+N₂→Sr₃N₂   [Scheme 1] 3Ca+N₂→Ca₃N₂   [Scheme 2]

Sr and Ca are nitrided in nitrogen atmosphere at a temperature from 600 to 900° C. for 5 hours. Sr and Ca may be either mixed and nitrided together or nitrided separately. Thus nitrides of Sr and Ca are obtained. Nitrides of Sr and Ca are preferably of high purity, but commercialized material may also be used.

The stock material Si is nitrided in nitrogen atmosphere. This reaction is represented by the following scheme 3. 3Si+2N₂→Si₃N₄   [Scheme 3]

Silicon Si is also nitrided in nitrogen atmosphere at a temperature from 800 to 1200° C. for 5 hours thereby to obtain silicon nitride. Silicon nitride used in the present invention is preferably of high purity, but commercialized material may also be used.

Nitrides of Sr and Ca, or nitride of Sr—Ca is crushed in a glove box in argon atmosphere or nitrogen atmosphere.

Nitride of Si is crushed similarly. Compound of Eu, Eu₂O₃, is also crushed similarly. While europium oxide is used as the compound of Eu, metal europium or europium nitride may also be used. In addition, imide compound or amide compound may be used as the material Z. Europium oxide is preferably of high purity, but commercialized material may also be used. Mean particle sizes of the nitride of alkaline earth metal, silicon nitride and europium oxide after crushing are preferably in a range from about 0.1 μm to 15 μm.

The materials described above may include at least one element selected from among a group consisting of Mg, Sr, Ca, Ba, Zn, B, Al, Cu, Mn, Cr, O and Ni. The elements described above such as Mg, Zn an B may be mixed while controlling the proportions in the mixing process described below. While these elements may be added into the stock material individually, they are usually added in the form of compounds such as H₂BO₃, Cu₂O₃, MgCl₂, MgO.CaO, Al₂O₃, metal boride (CrB, Mg₃B₂, AlB₂, MnB), B₂O₃, Cu₂O and CuO.

After the crushing processes described above, nitrides of Sr and Ca, or nitride of Sr—Ca, nitride of Si and Eu₂O₃ are mixed and Mn is added thereto. Since the mixture is easily oxidized, they are mixed in a glove box in Ar atmosphere or nitrogen atmosphere.

Last, the mixture of nitrides of Sr and Ca, or nitride of Sr—Ca, nitride of Si and Eu₂O₃ are fired in ammonium atmosphere, thus making a fluorescent material having composition of (Sr_(X)Ca_(1-x))₂Si₅N₈: Eu with Mn added thereto. Composition of the fluorescent material can be changed by changing the proportions of mixing the materials.

Firing can be done in a tubular furnace, compact furnace, induction furnace or metal furnace. While firing is carried out in a temperature range from 1200 to 1700° C., the temperature is more preferably from 1400 to 1700° C. Firing is preferably carried out in a single stage where the temperature is gradually raised and held in a range from 1200 to 1500° C. for several hours, 2-stage firing (multi-stage firing) may also be employed wherein first firing is carried out in a temperature range from 800 to 1000° C., then the temperature is gradually raised and held in a range from 1200 to 1500° C. for firing. The material to make the fluorescent material is preferably fired in a crucible or boat made of boron nitride (BN). Besides a crucible made of boron nitride, a crucible made of alumina (Al₂O₃) may also be used.

The desired fluorescent material can be obtained through the manufacturing method described above.

While nitride fluorescent material is used as the fluorescent material that emits reddish light, the present invention can provide a light emitting device comprising the YAG fluorescent material described above and the fluorescent material capable of emitting red light. The fluorescent material capable of emitting red light is a fluorescent material that is excited by light of wavelengths from 400 to 600 nm, for example Y₂O₂S: Eu, La₂O₂S: Eu, CaS: Eu, SrS: Eu, ZnS: Mn, ZnCdS: Ag, Al, ZnCdS: Cu, Al. Color rendering property of the light emitting device can be improved by using the YAG fluorescent material and the fluorescent material capable of emitting red light.

The fluorescent material capable of emitting red light represented by aluminum garnet fluorescent material and nitride fluorescent material formed as described above may be provided either in a plurality of kinds in the wavelength converting member constituted from a single layer on the surface of the light emitting device, or in a single kind or a plurality of kinds in the wavelength converting member constituted from two layers. This constitution makes it possible to obtain white light through blending of the light emitted by different fluorescent materials. In this case, it is preferable that the fluorescent materials have similar mean particle sizes and shapes in order to achieve satisfactory blending of the light emitted by the different fluorescent materials and minimize color unevenness. It is preferable to constitute the wavelength converting member such that the nitride fluorescent material is disposed nearer to the light emitting element than the YAG fluorescent material, in consideration of the fact that the nitride fluorescent material absorbs a part of the light that has undergone wavelength conversion by the YAG fluorescent material. This constitution prevents such a problem that the nitride fluorescent material absorbs a part of the light that has undergone wavelength conversion by the YAG fluorescent material, and makes it possible to improve the color rendering property of the blended light compared to a case where the YAG fluorescent material and the nitride fluorescent material are mixed. (Alkaline earth metal salt) The light emitting device may be provided with alkaline earth metal silicate activated with europium as the fluorescent material that absorbs a part of light emitted by the light emitting element and emits light of wavelength different from that of the absorbed light. The alkaline earth metal silicate is preferably ortho-silicate of alkaline earth metal represented by the following general formula. (2-x-y) SrO·x (Ba, Ca)O·(1-a-b-c-d)SiO₂·aP₂O₅bAl₂O₃cB₂O₃dGeO₂:y Eu²⁺ (where 0<x1.6, 0.005<y<0.5, 0<a, b, c, d<0.5) (2-x-y)BaO·x(Sr, Ca)O·(1-a-b-c-d)SiO₂·aP₂O₅bAl₂O₃cB₂O₃dGeO₂:y Eu²⁺ (where 0<x1.6, 0.005<y<0.5, 0<a, b, c, d<0.5) It is preferable that at least one of a, b, c and d is larger than 0.01.

As the fluorescent material made of alkaline earth metal salt, alkaline earth metal aluminate, Y(V, P, Si) O₄: Eu or alkaline earth metal-magnesium-dicilicate may be used, instead of the alkaline earth metal silicate described above. Me(3-x-y)MgSi₂O₃:xEu, yMn (where 0.005<x<0.5, 0.005<y<0.5, Me is Ba and/or Sr and/or Ca.)

Now the process of manufacturing the fluorescent material made of alkaline earth metal silicate according to this embodiment will be described below.

For the manufacture of alkaline earth metal silicate, alkaline earth metal carbonate, silicon dioxide and europium oxide are mixed in stoichiometrical proportions as the starting materials in accordance to the selected composition, and are transformed into the desired fluorescent material at temperatures 1100° C. and 1400° C., in reducing atmosphere through reactions of solid materials ordinarily employed in the manufacture of fluorescent materials. In this process, it is preferable to add less than 0.2 moles of ammonium chloride or other halogenide. A part of silicon may be substituted by germanium, boron, aluminum or phosphorus as required, and a part of europium may be substituted by manganese.

By combining the fluorescent materials described above, namely alkaline earth metal aluminate activated with europium and/or manganese, Y(V, P, Si) O₄: Eu or Y₂O₂S: Eu³+, emission of light having the desired color temperature and high color reproducibility can be achieved, as shown in Table 1. TABLE 1 Excitation Color wavelength Chromaticity Chromaticity Color temperature rendering Example Fluorescent material [nm] coordinate x coordinate y [K] property Ra 1 Sr_(1.4)Ba_(0.6)SiO₄ : Eu²⁺ 464 0.4619 0.4247 2778 72 2 Sr_(1.4)Ba_(0.6)SiO₄ : Eu²⁺ 464 0.4380 0.4004 2950 73 3 Sr_(1.6)Ba_(0.4)SiO₄ : Eu²⁺ 464 0.4086 0.3996 3497 74 4 Sr_(1.9)Ba_(0.08)Ca_(0.02)SiO₄ : Eu²⁺ 464 0.3762 0.3873 4183 75 5 Sr_(1.9)Ba_(0.02)Ca_(0.08)SiO₄ : Eu²⁺ 464 0.3101 0.3306 6624 76 6 Sr_(1.6)Ba_(0.4)SiO₄ : Eu²⁺ 464 0.3135 0.3397 6385 82 Sr_(0.4)Ba_(1.6)SiO₄ : Eu²⁺ 7 Sr_(1.9)Ba_(0.08)Ca_(0.02)SiO₄ : Eu²⁺ 464 0.3710 0.3696 4216 82 8 Sr_(1.6)Ba_(0.4)SiO₄ : Eu²⁺ 464 0.3756 0.3816 3954 84 Sr_(0.4)Ba_(1.6)SiO₄ : Eu²⁺ YVO₄ : Eu³⁺ 9 Sr_(1.6)Ba_(0.4)SiO₄ : Eu²⁺ 464 0.3115 0.3390 6489 66 Sr_(0.4)Ba_(1.6)SiO₄ : Eu²⁺ Barium magnesium aluminate : Eu²⁺ 10 Sr_(1.6)Ba_(0.4)(Si_(0.08)B_(0.02))O₄ : Eu²⁺ 464 0.3423 0.3485 5097 82 Sr_(0.6)Ba_(1.4)SiO₄ : Eu²⁺ 11 Sr_(1.6)Ba_(0.4)(Si_(0.08)B_(0.02))O₄ : Eu²⁺ 464 0.3430 0.3531 5084 83 Sr_(0.6)Ba_(1.4)SiO₄ : Eu²⁺ Strontium magnesium aluminate : Eu²⁺ 12 Sr_(1.4)Ba_(0.6)Si_(0.95)Ge_(0.05)O₄ : Eu²⁺ 464 0.4134 0.3959 3369 74 13 Sr_(1.4)Ba_(0.6)Si_(0.98)P_(0.02)O_(4.01) : Eu²⁺ 466 0.4630 0.4280 2787 72 14 Sr_(1.4)Ba_(0.6)Si_(0.98)Al_(0.02)O₄ : Eu²⁺ 464 0.4425 0.4050 2913 73 (Other Fluorescent Materials)

In this embodiment, fluorescent materials that are excited by ultraviolet rays and emits light of predetermined color may also be used such as listed below.

-   (1) Ca₁₀(PO₄)₆FCl: Sb, Mn -   (2) M₅(PO₄)₃Cl: Eu (where M represents at least one kind of element     selected from among Sr, Ca, Ba and Mg) -   (3) BaMg₂Al₁₆O₂₇: Eu -   (4) BaMg₂Al₁₆O₂₇: Eu, Mn -   (5) 3.5MgO.0.5MgF₂.GeO₂: Mn -   (6) Y202S: Eu -   (7) Mg₆As₂O₁₁: Mn -   (8) Sr₄Al₁₄O₂₅: Eu -   (9) (Zn, Cd)S: Cu -   (10) SrAl₂O₄: Eu -   (11) Ca₁₀(PO₄)₆ClBr: Mn, Eu -   (12) Zn₂GeO₄: Mn -   (13) Gd₂O₂S: Eu, and -   (14) La₂O₂S: Eu

These fluorescent materials may be used either individually or in a mixture thereof in the wavelength converting member constituted from a single layer, or individually or in a mixture thereof in the wavelength converting member constituted from two or more layers.

[Electrically Conductive Wire 104]

Connection between the electric wiring 105 formed in the recess of the package and the electrodes of the LED chip 103 can be made by disposing the electrodes of the LED chip 103 to oppose the electric wiring 105 via electrically conductive wires or electrically conductive members. The electrically conductive wires 104 is a kind of electrical connecting member that connects the electrodes of the LED chip 103 and the electric wiring 105 formed in the ceramics package, and is required to have good ohmic property, good mechanical connection, high electrical conductivity and high thermal conductivity. Thermal conductivity is preferably 0.01 cal/cm²/cm/° C. or higher, and more preferably 0.5 cal/cm²/cm/° C. or higher. Diameter of the electrically conductive wire is preferably in a range from 10 μm to 45 μm, in consideration of workability. The electrically conductive wire may be made of such metal as gold, copper, platinum or aluminum, or an alloy thereof. Such an electrically conductive wire can connect the electrodes of the LED chip and the electric wiring formed on the substrate easily by means of a wiring bonding tool. Now examples of the present invention will be described in detail below. It should be noted that the present invention is not limited to these examples.

EXAMPLE 1

Example 1 of the present invention will be described with reference to the accompanying drawings. FIG. 1A is a schematic top view of a light emitting device 100 that uses the ceramics package and the light emitting element according to this embodiment. FIG. 2 is shows a sectional view taken along lines C-C′ in FIG. 1 and an enlarged sectional view of a portion around the top face of the recess side wall. FIG. 1B is a perspective view schematically showing the semiconductor device of this embodiment being electrically and mechanically connected by soldering to the mounting surface where the wiring pattern has been formed.

The ceramics package of this embodiment comprises at least a ceramics base 202 serving as the substrate, and a ceramics base 204 having through hole that widens toward the opening. The ceramics base 202 that serves as the substrate has the electrical wiring 105 for supplying power to the LED chip 103 running from the bottom of the recess on the package through the ceramics bases 202, 203 to extend to the outer surface of the light emitting device. The electrical wiring 105 is exposed in the recess on the package, and the electrical wiring 106 is exposed on the cleavage surface of the ceramics substrate. The electrical wiring 106 that is exposed to extend over the outer surface of the light emitting device is connected to the electrical circuit provided on the mounting substrate when the light emitting device is mounted so that the side face adjacent to the light emitting surface is disposed to oppose the mounting substrate. The inner wall surface of the ceramics base that expands toward the opening forms the recess of the package, with the reflecting surface 102 formed thereon. The light emitting device of this embodiment further has a sealing member that seals the recess of the ceramics package. The electrical wiring 105 and the reflecting surface 102 comprise a resin paste (about 30000 ps in viscosity) containing tungsten (mean particle size about 1 μm) and coated with Ag. The LED chip 103 is secured with an insulating adhesive on the surface of the electrical wiring 105 provided on the bottom of the recess in the package.

Now formation of the ceramics package of this embodiment will be described below. First, a green sheet made mainly of alumina is cut into a predetermined size, to make a precursor of the ceramics base 202. A resin paste containing tungsten is screen-printed in the pattern of the electrical wiring 105.

A green sheet having a through hole of a size enough to accommodate the LED chip and a green sheet having a through hole expanding toward one opening are formed. A resin paste containing tungsten is screen-printed in the shape of the reflecting surface 102 on the green sheets, to make the precursors of the ceramics base 204.

The plurality of green sheets formed as described above are placed one on another while aligning the though holes, and are processed by heat pressing in vacuum to form the recess.

Through holes 0.3 mm in diameter are formed by the ordinary method using a punching machine. The through holes are formed at least in a pair and, in this embodiment, two through holes are formed for each of positive and negative electrodes. The through holes are then filled with the resin paste containing tungsten by screen printing, so as to form the electrical wiring 106 exposed on the outer surface of the ceramics package.

Scribe lines are formed in a predetermined pattern on one of the principal surfaces of the green sheet stack. The grooves are formed in the shape of matrix so that the recess is included between the groove formed in the longitudinal direction and the groove formed in the lateral direction of the ceramics substrate. After forming the grooves, the ceramics stack is sintered to made the ceramics substrate. The paste containing tungsten is turned into a first metal layer by sintering. Then the exposed surface of the first metal layer is covered by an Ni/Ag multi-layer film that becomes a second metal layer by plating. Thus the reflecting surface 102 and the electrical wirings 105, 106 are formed to complete the ceramics substrate having the recess 2.0 mm in diameter and 0.8 mm in depth.

The LED that is a semiconductor light emitting element is made of InGaN semiconductor with main emission peak at wavelength 450 nm. The LED chip is made by forming a gallium nitride semiconductor by MOCVD method while flowing TMG (trimethyl gallium) gas, TMI (trimethyl indium) gas, nitrogen gas and dopant gas together with a carrier gas over a cleaned sapphire substrate. PN junction of gallium nitride semiconductor having N-type conductivity and gallium nitride semiconductor having P-type conductivity is formed by switching between SiH₄ and Cp₂Mg to be flowed as the dopant gas. The P-type semiconductor is annealed at a temperature of 400° C. or higher after forming the layer.

After exposing the P-type and N-type semiconductors by etching, the electrodes are formed by sputtering. The semiconductor wafer thus made is scribed to form lines along which the wafer is cleaved by an external force and separated into LED chips. The LED chip capable of emitting blue light is die-bonded onto the bottom of the recess of the ceramics package with epoxy resin that is then heated to harden. Then the electrodes of the LED chip and the electrical wirings are electrically connected by wire bonding using electrically conductive wires made of gold. The recess in the ceramics substrate wherein the LED chip is mounted is filled with silicone resin to form the sealing member. The silicon resin is poured up to near the top face of the recess side wall of the ceramics package and is hardened. Part of the silicone resin either impregnates the side wall of the recess or creeps up to the top surface before being hardened. For example, the silicone resin is concentrated around the recess viewed from the light emission observing side, and a part of the silicone resin extends to the ceramics portion on the top face of the recess side wall as shown in FIG. 2. The extended portion, while it depends on the viscosity of the silicone resin and on the extent to which the ceramics is sintered, creeps from the recess to the top face of the recess side wall as indicated by the extended portion Y in the enlarged sectional view of FIG. 2. A part of the silicone resin also impregnates the porous ceramics that constitutes the side wall. The impregnated portion is indicated by the impregnated portion X in the enlarged sectional view of FIG. 2, although it depends on the viscosity of the silicone resin and on the extent to which the ceramics is sintered.

FIG. 3A through FIG. 3C are side views schematically showing the processes of manufacturing the ceramics package according to this embodiment. Bending moment is applied to the fired stack of green sheets (ceramics substrate) around the point on the surface opposite to the groove, while applying a tensile force in the direction parallel to the principal surface, thereby separating the ceramics substrate. This enables it to cleave the substrate along the shortest path from the groove to the back surface, thereby minimizing the generation of burrs and chippings. In the present invention, since the tensile force is applied simultaneously with the bending moment, the mating cleavage surfaces hardly rub against each other. While the ceramics can be broken with only a tensile force, it requires a great magnitude of force, so that it becomes necessary to make the grooves deeper or sandwich the ceramics substrate. Forming the grooves deeper leads to such troubles as cracking during polishing in a carrying step or working step. Sandwiching the ceramics substrate may also roughen the surface of sandwiched portion. Although the ceramics substrate can be cleaved by applying the bending moment only, the mating cleavage surfaces rub against each other making it more likely that chipping and breakage occur in the cleavage surfaces. Also because the ceramics substrate is cleaved in the portion where it is easier to break, it becomes easier for burrs to occur.

Now the method of forming the ceramics package according to this embodiment will be described in detail below. As shown in FIG. 3A, a pair of stages 114 which can move in directions opposite to each other are disposed to oppose each other. Then the ceramics substrate 109 is disposed to bridge the pair of stages 114 so that the groove 108 is located at the portion where the pair of stages 114 oppose each other. Last, as shown in FIG. 3B, a cleavage tool 112 is pressed against the substrate at the position corresponding and opposite to the groove, and the pair of stages 114 are moved in the opposite directions (in the direction in which the tensile force is exerted).

The ceramics substrate is separated first in the longitudinal direction of the ceramics package, then in the lateral direction, thereby separating into individual ceramics packages. (At this time, the ceramics substrate 109 is preferably covered with an adhesive sheet 115 on the side thereof where the groove and the recess are formed. This makes it possible to prevent ceramics dust generated during the cleaving process from depositing on the sealing member made of silicone resin, and improve the bonding of the elastic body 113 with the ceramics substrate 109.) The ceramics substrate 109 is placed on the elastic body 113 via the adhesive sheet 115. This configuration improves the bonding between the elastic body 113 and the ceramics substrate 109 during the cleaving process. At the same time, the ceramics substrate 109 is placed on the stage 114 via the elastic body 113. With this configuration, the elastic body 113 deforms when the cleaving tool 112 is applied, and bending moment 110 is applied when the cleaving tool 112 is pressed against the substrate toward the groove.

Cleaving the substrate as described above makes it possible to form the light emitting device without causing chipping or burrs in the cleavage surface. The light emitting device of this embodiment can be used as sideways emission type light emitting device utilizing the cleavage surface of the ceramics package as the mounting surface for the external circuit board, thus making it possible to cause light to enter the optical guide plate without variations in the mounting accuracy.

As shown in FIG. 1B, the light emitting device 100 of this embodiment is electrically and mechanically connected by means of solder 116 to the mounting surface 117 of the substrate provided with the electrical circuit.

The silicone resin impregnates the ceramics base 205 that constitutes the principal surface on the light emission observing side of the ceramics package, or extends from the recess. The solder applied on the mounting surface 117 during the reflow process is restricted from creeping up toward the light emitting surface by the silicone resin provided on the principal surface on the light emission observing side, so that such troubles do not occur as the solder lines contact with each other or the solder covers the opening of the recess of the ceramics package. Thus the light emitting device 100 of this example can be connected to an external circuit board with high reliability.

EXAMPLE 2

FIG. 8 is a schematic sectional view of the light emitting device of this example. The sealing member 107 of this example is formed so as to cover at least the light emitting element 103 without covering the reflecting surface 102. As indicated by Y in the enlarged sectional view of FIG. 8, the silicone resin covers the top face of the recess side wall of the ceramics package. In addition, a part of the silicone resin impregnates the ceramics base 204 that forms the top face of the recess side wall and forms an impregnated portion X. In this example, since the solder is restricted from creeping up by the silicone resin that covers the top face of the recess side wall, the solder that has been reflowed never touches the reflecting surface 102. Therefore, mounting can be carried out with high reliability as short-circuiting does not occur between positive and negative electrodes when mounting the device on an external circuit board that has electrical circuit formed thereon.

EXAMPLE 3

The light emitting device of this example is formed similarly to Examples 1 and 2, except for containing fluorescent material in the sealing member.

Stock material for the fluorescent material is made by coprecipitating a solution of a mixture of rare earth elements Y, Gd, Ce in stoichiometrical proportions dissolved in an acid with oxalic acid, firing the product of coprecipitation to obtained a coprecipitated oxide, and mixing it with aluminum oxide. This mixture, with a fluoride such as ammonium fluoride added thereto as a flux, is put into a crucible and fired at a temperature of about 1400° C. in air for three hours. The fired mixture is crushed in a ball mill in wet process, and undergoes the processes of washing, separation, drying and sieving, thereby to obtain a fluorescent material (Y_(0.995)Gd_(0.005))_(2.750)A₁₅O₁₂:Ce_(0.250) having median particle size of 8 μm.

5.5% by weight of the fluorescent material (refractive index 1.84) is added to the silicone resin composition (refractive index 1.53) and mixed for about five minutes. The thermosetting material thus obtained is put into the recess of the ceramics package to fill in. Last, heat treatment is applied at 70° C. for 2 hours and at 150° C. for 1 hour. This makes it possible to provide the light emitting device that can blend the light emitted by the light emitting element and the light emitted by the fluorescent material that absorbs the light emitted by the light emitting element and emits light of different wavelength. Particularly by containing the fluorescent material in the sealing member 107 of Example 2, the reflecting surface 102 can reflect the blended light efficiently toward the light emission observing side.

EXAMPLE 4

FIG. 5 is a top view of the ceramics package of this example. The ceramics package of this example has the recess for mounting the light emitting element therein. A pair of positive and negative leads 107 a, 107 b are provided in the bottom of the recess, where the ceramics base 206 is exposed so as to isolate the pair of positive and negative leads 107 a, 107 b. The semiconductor element is placed at the center of the bottom of the recess where the ceramics is exposed, while part of the electrical wire 107 a is formed so as to surround the semiconductor element. In case the transparent substrate side of the semiconductor light emitting element that is made by stacking the semiconductor on a transparent substrate such as a sapphire substrate is mounted to oppose the bottom of the recess, the transparent substrate is preferably covered with a metal that has high reflectivity to light such as Al, Ag or an alloy thereof. This constitution makes it possible to reflect the light that would otherwise be transmitted through the ceramics toward the light emission observing side, thereby improving the efficiency of extracting light from the light emitting device. Another semiconductor element such as protective element may also be mounted on the electrical wire. Exposed on the side face of the ceramics package are a pair of positive and negative leads 108 a, 108 b that are connected to the pair of positive and negative leads 107 a, 107 b. In the ceramics package 200 of this example, unlike the examples described above, ceramics having through hole of smaller diameter is located at the outermost position of the recess side wall. Therefore, although the ceramics package of this example has the reflecting surface on the inner surface of the recess that expands toward the opening similarly to the examples described above, it cannot be seen in the top view of FIG. 5. In addition, a pair of marks 207 that indicate the cathode position are printed on a corner of the principal surface on the light emission observing side of the ceramics package of this example. The pair of marks 207 that indicate the cathode position can be formed by printing a resin paste containing tungsten on the ceramics green sheet and firing it.

EXAMPLE 5

FIG. 6 is a top view of the ceramics package of this example. The ceramics package of this example is similar to that of Example 3 except for the different pattern of the electrical wiring provided on the bottom of the recess. Specifically, the pair of positive and negative leads 107 a, 107 b are formed in two pairs so as to oppose each other when viewed from the light emission observing side. The semiconductor element is placed at the center of the bottom of the recess where the ceramics is exposed, while part of the electrical wire is formed so as to surround the semiconductor element. Area of the ceramics base 206 that is exposed between the pair of positive and negative leads 107 a, 107 b is made larger than that in Example 3. Strength of adhesion is higher between the ceramics and the sealing member than between the electrically conductive wire and the sealing member. Therefore, constitution of this example makes it possible to improve the strength of adhesion between the ceramics package and the sealing member, so as to provide the semiconductor device having high reliability where the sealing member does not peel off.

EXAMPLE 6

FIG. 7 is a top view of the ceramics package of this example. The ceramics package of this example is similar to those of Examples 3 and 4 except for the different pattern of the electrical wiring provided on the bottom of the recess. Specifically, the pair of positive and negative leads 107 a, 107 b are formed in two pairs so as to oppose each other when viewed from the light emission observing side. Area of the ceramics base 206 that is exposed between the pair of positive and negative leads 107 a, 107 b is made larger than that in Example 4. The constitution of this example, in addition to the effects of the present invention described above, further improves the strength of adhesion between the ceramics package and the sealing member than in the case of Example 4, so as to provide the semiconductor device having high reliability where the sealing member does not peel off.

COMPARATIVE EXAMPLE

FIG. 10A is a top view of the ceramics package of this example. FIG. 10B is a sectional view taken along lines X-X in FIG. 10A. In the ceramics package of the comparative example, grooves are formed by incising the ceramic substrate to a depth of ½ of the thickness of the ceramics substrate. A bending moment is applied from the side opposite to the side where the grooves are formed. Some of a number of pieces have a cleaved face as shown in FIG. 10A. The portion cleaved vertically has a protruded portion protruding out from a vertical face extending vertically from the incised portion toward the opposite side to the side to be mounted with the semiconductor element are more than half of the thickness of the ceramics substrate. In a sideways emission type light emitting device in which this support body is used, a tilt on mounting is more than 30 degree since the protruded portion A is larger than half of the thickness of the ceramics substrate. With this, emitting angles vary for each product and defective products are produced.

Contrast with this, since the dent portion B do not affect the tilt on mounting, the denting depth may be more than half of the thickness of the ceramics substrate. If the mounting surface has a dent portion B, there is no problem because the tilt on mounting is not affected. However, the productivity is degraded extremely, since the cleaved surface of the ceramics package which was adjacent before cleaving has the protruded portion A which would fit to the dent portion B. Therefore, from the viewpoint of productivity, the production method according to present invention is preferably used so that the depth of the dent portion is half of the thickness of ceramics substrate or smaller, preferably quarter of the thickness of the ceramics substrate or less, more preferably {fraction (1/10)} of the thickness of the ceramics. substrate or less.

The ceramics package of the present invention can be used as a support body For a semiconductor device that comprises a light emitting element or a light receiving element. The light emitting device that employs the ceramics package of the present invention can be used as a sideways emission type light emitting device. 

1. A support body capable of supporting a semiconductor element, that is made by cleaving a ceramics substrate whereon electrical conductors are disposed, wherein a side face of the support body has a incised portion located on the side where the semiconductor element is to be mounted, and a portion cleaved substantially at right angles from the incised portion by applying a bending moment and a tensile force substantially simultaneously to the ceramics substrate, wherein the incised portion is in a range from ¼ to ¾ thickness of the ceramics substrate.
 2. The support body according to claim 1, characterized in that a protruded portion protruding out from a vertical face extending vertically from the incised portion toward the opposite side to the side where the semiconductor element is to be mounted are half of the thickness of the ceramics substrate or smaller in the portion cleaved at right angles.
 3. The support body according to claim 1, characterized in that the support body has a recess for housing the semiconductor element, and the electrical conductor is disposed either in a part of or the entire recess.
 4. The support body according to claim 1, characterized in that side face of the support body has a metal disposed at least on one of the corners so as to extend from the surface where the semiconductor element is to be mounted to the back surface.
 5. A semiconductor device comprising a semiconductor element and a support body whereon the semiconductor element is mounted, said support body being made by cleaving a ceramics substrate whereon electrical conductors are disposed, wherein a side face of the support body has a incised portion located on the side where the semiconductor element is to be mounted, and a portion cleaved substantially at right angles from the incised portion by applying a bending moment and a tensile force substantially simultaneously to the ceramics substrate, wherein the incised portion is in a range from ¼ to ¾ thickness of the ceramics substrate.
 6. The semiconductor device according to claim 5, wherein said support body has a recess for housing a semiconductor element, and the electrical conductor is disposed in a part of the recess, while the side face of the support body has a metal disposed at least on one of the corners so as to extend from the surface where the semiconductor element is mounted to the back surface, and the recess and top face of the recess side wall are covered with a resin.
 7. The semiconductor device according to claim 6, wherein a top face of the recess side wall is covered with a resin in a portion of the ceramics base.
 8. The semiconductor device according to claim 6, wherein the inside of said recess and the top face of the recess side wall are impregnated with a resin in a portion where the ceramics base is exposed.
 9. A method of manufacturing a support body capable of supporting a semiconductor element, comprising processes of making a ceramics substrate by stacking ceramics sheets with electrical conductors disposed thereon, incising the ceramics substrate thereby forming a groove, and cleaving the ceramics substrate along the grooves, wherein the ceramics substrate is cleaved by applying a bending moment and a tensile force to the ceramics substrate.
 10. The method of manufacturing the support body according to claim 9, wherein the bending moment is applied by bringing a cleaving tool into contact with the surface opposite to the surface having the grooves of the ceramics substrate at a position corresponding to the groove.
 11. The method of manufacturing the support body according to claim 9, wherein the ceramics substrate is cleaved by applying a bending moment in such a manner as the substrate becomes concave on the side thereof where the groove is formed so that the opposing top edges of the recess side walls make contact with each other.
 12. The method of manufacturing the support body according to claim 9, wherein the grooves of the ceramics substrate are formed in the longitudinal and lateral directions on the front surface, and wherein through holes are made at the intersects of the longitudinal and lateral grooves.
 13. The method of manufacturing the support body according to claim 9, wherein the ceramics substrate is provided with a plurality of through holes along which the grooves are formed on the surface of the ceramics substrate.
 14. The method of manufacturing the support body according to claim 9, wherein the ceramics substrate is fired to form a groove after incising the ceramics substrate to a depth in a range from ¼ to ¾ thickness of the ceramics substrate.
 15. The method of manufacturing the support body according to claim 9, wherein ceramics sheets having electrical conductors disposed thereon are stacked one on another to form a ceramics substrate having a recess formed therein, which is cleaved along grooves formed along the side walls of the recess, thereby making the support body that have the electrical conductors exposed on the cleavage surface and in the recess.
 16. A semiconductor device comprising the semiconductor element and the support body made of a stack of ceramics layers having the recess in which the electrical conductors are electrically connected with the semiconductor element, wherein at least a part of the top face of the recess side wall is covered by a resin.
 17. The semiconductor device according to claim 16, wherein said resin is caused to further impregnate the ceramics base portion of the side wall of the recess.
 18. The semiconductor device according to claim 16, wherein the semiconductor element is coated with the resin and a part of the resin is disposed to extend over the top face of the recess side wall.
 19. The semiconductor device according to claim 16, wherein the resin contains at least one kind of fluorescent material selected from among a fluorescent material that contains Al and at least one element selected from among Y, Lu, Sc, La, Gd, Tb, Eu, Ga, In and Sm, and is activated with at least one element selected from among rare earth elements, and a fluorescent material that contains N, at least one element selected from among Be, Mg, Ca, Sr, Ba and Zn and at least one element selected from among C, Si, Ge, Sn, Ti, Zr and Hf, and is activated with at least one element selected from among rare earth elements. 